Sliding contact cam and tappet

ABSTRACT

A RECIPROCABLY MOUNTED TAPPET ADAPTED TO BE INTERMITTENTLY ACTUATED BY A ROTATABLE CAM HAS A NON-FLAT CAMCONTACTING SURFACE CONTOURED AS TO ACHIEVE BOTH DESIRED TAPPET LIFT VELOCITY AND A FULL CAM WIDTH CONTACT THEREACROSS.

Oct. 5, 1971 E. J. REPEN SLIDING CONTACT CAM AND TAPPET Filed June 4., 1969 INVENTOR. 5014 4/90 J PEPE/V 0 A T TOR/VEY United States Patent 3,610,057 SLIDING CONTACT CAM AND TAPPET Edward J. Repen, Warren, Mich., assignor to Holley Carburetor Company, Warren, Mich. Filed June 4, 1969, Ser. No. 830,233 Int. Cl. F1611 /08; F01] l /00 US. Cl. 74-55 4 Claims ABSTRACT OF THE DISCLOSURE A reciprocably mounted tappet adapted to be intermittently actuated by a rotatable cam has a non-fiat camcontacting surface contoured as to achieve both desired tappet lift velocity and a full cam width contact thereacross.

BACKGROUND OF THE INVENTION In fuel injection systems, both diesel as well as gasoline, it is often accepted practice to employ a fuel pumping and metering assembly which is comprised essentially of a plurality of individual fuel pumping or injecting plunger assemblies (often one such plunger assembly for each cylinder of the associated engine) which are sequentially actuated in pumping and discharging strokes by a cam shaft assembly rotated in timed relation to the said engine.

In such arrangements the plunger assemblies have often been provided with a roller type cam follower, this being done primarily to minimize Wear between the cam and cam follower, and to obtain desired plunger motion and velocity. However, such roller type followers are very costly and usually consist of many individual parts or components each of which presents problems of space and a possible source of subsequent structural failure.

In the past attempts have been made to replace such roller type followers with flat-faced sliding contact tappets; however, such attempts have not proved to be practical because it was not possible to obtain the desired plunger motion and velocity. In fuel injection systems, it is desirable to have the plunger traveling at a high velocity during that portion of its stroke in which fuel is being injected. This plunger velocity, in the case of fiatfaced tappets, is proportional to the radial distance from the cam and tappet point of contact to the vertical centerline through the tappet and cam centerline. Attempts to obtain higher plunger velocities, as by enlarging the diameter of the tappet in order to thereby increase the radial distance from the cam and tappet contact point to tappet centerline, have not been acceptable because of the resulting increase in the overall size of the tappet. This increase in size, in turn, required substantially greater center-distances, as between successively spaced tappets and related plunger assemblies, and such increased centering-distances were found to be prohibitive for a commercially acceptable fuel injection system.

Accordingly, the invention as herein disclosed and claimed is concerned with the solution of the above as well as other related problems.

SUMMARY OF THE INVENTION The invention as herein disclosed comprises a sliding contact cam and tappet arrangement including a rotatable cam and a reciprocable tappet, said cam including an actuating cam surface of definable width, and said tappet including a cam-engaging surface for engaging said actuating surface, said cam-engaging surface having a contoured curvilinear profile.

Accordingly, a general object of this invention is to provide, in a sliding contact cam and tappet arrangement, a tappet having a cam-engaging surface of a profile which Wee will assure the attainment of a full cam width contact thereacross from the start to the finish of the sweep of the cam across the tappet face and obtain the desired plunger velocity and motion.

Other more specific objects and advantages of the invention will become apparent when reference is made to the following detailed description considered in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein for purposes of clarity, certain of the details may be omitted from one or more views:

FIG. 1 is a perspective view of a typical fuel injection metering assembly, with portions thereof broken away and in cross-section;

FIG. 2 is an enlarged fragmentary cross-sectional view taken generally on the plane of line 22 of FIG. 1 and looking in the direction of the arrows;

FIG. 3 is somewhat a diagrammatic View illustrating by comparison a tappet constructed in accordance with the invention and a flat-faced tappet of the prior art; and

FIG. 4 is an end projection of FIG. 3, taken generally on the plane of line 44 of FIG. 3, including diagrammatic representations thereon of comparative contact patterns developed by the cam on the end of the tappet of the invention as well as the tappet of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in greater detail to the drawings, FIG. 1 illustrates a fuel injection pump assembly 10 having a housing 12 and provided with a plurality of cam-actuated fuel injecting plunger assemblies 14, 16, 18, 20, 22 and 24 FIG. 2, a cross-sectional view taken on the plane of line 22 of FIG. 1, illustrates the plunger assembly 16, fragmentarily, as comprising a solid cylindrical tappet 26 slidably received within a cylindrical passageway 28 formed in the housing 12. A spacer or backing plate 30, received within tappet 26, has a plunger stem 32 and spring retainer 34 urged thereagainst as by a coiled compression spring 36. A suitable stem guide is fragmentarily illustrated at 38. A suitable elongated guide slot 40, formed in the wall of tappet 26, may be provided to closely receive therein the cylindrical keying portion 42 of a lock or keeper screw 44 threadably secured in the housing 12.

A cam shaft 46, suitably journalled within housing 12, carries a plurality of cams, one of which is illustrated at 48. As cam shaft 46 rotates about its axis A, cam 48 is correspondingly rotated causing the tappet 26 to be alternately moved upwardly (thereby pumping fuel to the associated engine) and resiliently moved downwardly by spring 36 in what may be generally described as an intake stroke. Such action occurs with the tappet face 50 being held against and in sliding contact with the cam surface 52.

In FIG. 3, points K and K describe one circular arc of the cam surface 52; further, for purposes of illustration let it be assumed that point K is a common point of contact between tappet face 50 and cam surface 52. Line 54 of a line of centers connecting point C and centerline A, where point C, is the center of the radius used to describe surface 50. Point C is the center of the cam nose radius.

A straight line 56 drawn through points C K C will intersect at a point C a second straight line 58 drawn through point A, and perpendicular to the line through C and A. Accordingly, it can be seen that point K reppresents the point of maximum eccentricity of the point of contact on the cam and tappet, and that line C -A is also at its maximum length. Since line C A is proportional to plunger velocity, this velocity is also at a maximum. If now point K is projected onto FIG. 4 (a bottom end view of tappet 2 6 taken generally on the plane of line 44) a line of contact 60 joining point K with point K can be established on the surface 50. In FIG. 4 horizontal phantom lines 62 and 64 designate the respective opposed axially spaced end surfaces of cam 48 so as to define therebetween the effective width of the cam surface 52. Accordingly, it can be seen that line-of-contact 60 is located well within the outer diameter 66 of tappet 26.

Now, in comparison, let the prior art type of tappet 26a be considered. As illustrated in dash line in FIG. 3, tappet 26a has a flat end face or cam engaging surface 50a and the outer diameter of tappet 26a is assumed to be the same as that of tappet 26. Accordingly, the projected area of surface 50a as generally depicted in FIG. 4 would be the same as that of surface 50.

Now with prior art tappet 26a situated as shown in FIG. 3 and cam 48 rotated to the dash line position at 48a so that line C A is the same as above, the following changes and relationships will occur. Point K on cam surface 52 has rotated to assume the position shown at H and the center of nose radius C has rotated to the position, C Consequently, line 56a passing through points C and C also passes through point H and thereby establishes the maximum eccentricity of the point of contact H on the cam and tappet surfaces. Therefore, if point H is now projected onto FIG. 4 a theoretical line of contact 68 falls well outside of the outer diameter 66a of the tappet 26a. Accordingly, since the maximum eccentricity of theoretical line 68 lies beyond the outer diameter of the tappet 26a, the flat-face tappet and cam would have to be redesigned to prevent this undesirable condition with a resulting decrease in maximum plunger velocity.

Further, with a flat face cam-engaging surface as 50a it is impossible to tailor the cam and follower combination in order to produce the required characteristics relating to tappet velocity, acceleration and load within the usual limits of the size of that particular tappet. This is in contrast to the invention which makes its possible to both achieve full width cam surface contact and the required characteristics of tappet velocity, acceleration and displacement by correspondingly tailoring the cam and contouring the tap cam engaging surface.

In the form of the invention specifically disclosed, tappet face 50 has been contoured to have a curvilinear profile which, in effect, is a cylindrical sector; as such the curvature of surface 50 is a constant radius equivalent to the length represented between points C and K However, it should be apparent that surface 50 could be contoured so as to have a curvilinear profile which, if of a single continuous radius, could have its center of curvature eccentrically disposed with respect to the axis 54. Further, surface 50 could be contoured so as to have a curvilinear profile which is formed by a series of joined arcuate sections or sectors of differing radii. Also the vertical center line of the tappet through C need not 6 pass through A. The determination of the precise nature of the curvilinear profile will, of course, be dependent on the particular performance characteristics required of the tappet.

Although only one preferred embodiment of the invention has been disclosed and described, it is apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

I claim:

1. A sliding contact cam and tappet arrangement, comprising a rotatable cam with an axis of rotation and an eccentric tappet-displacing portion having opposed convex curvilinear portions joined by a nose portion, said cam having width and the first peripheral surfaces there of being parallel to said axis of rotation, a cylindrical tappet member having a convex curvilinear second surface at the cam-engaging end thereof, the projection of said second surface on a plane perpendicular to the axis of said tappet being a circle and said second surface being parallel to said peripheral surfaces of said cam, the relationship of said first and second convex curvilinear surfaces being such that the projection of the sliding line contact between said cam and tappet on said plane being a rectangle falling entirely within said circle, whereby the maximum eccentricity of contact between said cam and said tappet is represented by those opposite sides of said rectangle which are parallel to the axis of rotation of said cam.

2. A sliding contact cam and tappet arrangement such as that recited in claim 1, wherein the opposite sides of said rectangle rep-resenting said maximum eccentricity parallel to the peripheral surfaces of said cam.

3. A sliding contact cam and tappet arrangement such as that recited in claim 1, wherein, on a plane through the axis of said tappet perpendicular to said axis of rotation of said cam, a line between the center of curvature of said second surface and the point of contact between said cam and said tappet intersects a line through said axis of rotation normal to said axis of said tappet at a distance from said axis of rotation that is proportional to tappet velocity.

4. A sliding contact cam and tappet arrangement such as that recited in claim 1, wherein, on a plane through the axis of said tappet perpendicular to said axis of rotation of said cam, the relationship of said cam and tappet designs are such that when the centers of curvature of said second surface and said cam nose and the point of contact between said cam and said tappet define a straight line, a condition of maximum eccentricity giving maximum lift velocity of said tappet exists.

References Cited UNITED STATES PATENTS 1,983,744 12/1934 Dock 74-55 2,423,701 7/1947 Hardy 74-55 2,706,973 4/1955 Russell 7455 2,935,878 5/1960 Wirsching 7455 2,908,261 10/1959 Van Duen l2390.49

WILLIAM F. ODEA, Primary Examiner W. S. RATLIFF, JR., Assistant Examiner U.S-. Cl. X.R. 12390.49 

